Circuit configuration comprising a control loop

ABSTRACT

A circuit arrangement is disclosed with a regulating circuit which is particularly used for regulating a resonant converter having a plurality of outputs. The arrangement includes a protective circuit that can be constructed with the least possible circuitry and cost. The regulating circuit is used for generating a pulse-width modulated regulation signal (20) in dependence on measuring signals (Va, Vb) present on inputs of the regulating circuit (20). The arrangement further includes a comparator circuit (212) for comparing the duty cycle (δ) of the regulation signal (20) with a predefinable maximum duty cycle value (δmax) and minimum duty cycle value (δmin), in which in case of a duty cycle (δ) situated outside the range between the maximum duty cycle value (δmax) and the minimum duty cycle value (δmin) the circuit arrangement delivers control information that corresponds to this exceeding of the range.

The invention relates to a circuit arrangement with a regulating circuitwhich is particularly used for regulating a resonant converter having aplurality of outputs.

In resonant converters a DC voltage carried on the input side is firstchopped and the AC voltage thus produced in the form of a chopped DCvoltage is processed by means of circuit parts containing resonantcircuit elements.

Transformers, particularly ones that produce an electrical separation ofthe input and output side of the converter are used for this purpose.With converters of this type it is possible to manufacture inexpensive,small and light-weight power supply units/switched-mode power supplies,which can advantageously be used in consumer electronics appliances suchas set top boxes, satellite receivers, television sets, computermonitors, video recorders and compact audio systems. In theseapplications there is often a need for converters that generate multipleoutput voltages on multiple converter outputs from one input DC voltage.

In German patent application no. 101 22 534.2 (data of filing Sep. 5,2001) is described a resonant converter which has a plurality of outputsand comprises a transformer having one primary winding and at least twosecondary windings having different winding orientations. The converteralso includes a regulating circuit for regulating the converter outputvoltages.

A known concept for a converter protection circuit includes the use ofsecondary side fuses which are gone when they are overloaded. Before theconverter is operated again, the fuses that have blown are to bereplaced by new fuses.

It is an object of the invention to provide a circuit arrangementcomprising a regulating circuit for converters having a plurality ofoutputs, which circuit arrangement includes a protective circuit thatcan be manufactured with the least possible circuitry and expense andcalculation effort which is a reliable protection against cases ofoverload.

The object is achieved by a circuit arrangement comprising a regulatingcircuit which is used for generating a pulse-width modulated regulationsignal in dependence on two measuring signals present on inputs of theregulating circuit, and including a comparator circuit for comparing theduty cycle of the regulating circuit with a predefinable maximum andminimum duty cycle value, while in case of a duty cycle situated outsidethe range between the maximum duty cycle value and the minimum dutycycle value the circuit arrangement delivers control information thatcorresponds to this exceeding of the range.

In case of overload this circuit arrangement is in a position toreliably switch off a converter. The protective circuit can beconstructed with few cost-effective components.

The control information is delivered more particularly by simplyswitching off the regulation signal i.e. setting the regulation signalto the zero value (claim 2); other variants would be here thetransmission of the digital signal within the regulation signal or thedelivery of a control signal via a separate output of the circuitarrangement. The claims 3 to 5 characterize an overvoltage protectionwhich is a precise and reliable protection against overvoltages andco-operates with the overload protective circuit. Claim 6 makes afeedback loop possible with which even if an optocoupler fails there isstill a feedback path available for transmitting feedback signals whichcause the connected converter to be switched off.

The invention also relates to integrated circuits which include parts ofthe circuit arrangement according to the invention (claims 7 to 9).

Furthermore, the invention relates to a resonant converter whichincludes the circuit arrangement according to the invention and/or atleast one of the integrated circuits according to the invention (claim10).

The invention will be further described with reference to examples ofembodiment shown in the drawings, to which, however the invention is notrestricted. In the drawings:

FIG. 1 shows a resonant converter having two outputs,

FIG. 2 shows a half-bridge circuit for the resonant converter,

FIGS. 3A, 3B and 3C show various output filters for the resonantconverter,

FIG. 4 shows an equivalent circuit diagram for the resonant converter,

FIGS. 5 to 7 show voltage and current curves in the resonant converter,

FIGS. 8 to 10 show various options of embodiments for a resonantconverter according to the invention,

FIG. 11 shows an example of the coupling of converter outputs to theregulating circuit of the resonant converter,

FIG. 12 shows a block diagram for a design variant of the regulatingcircuit of the resonant converter and

FIG. 13 shows a block diagram for a regulating circuit with overvoltageand overload protection circuits.

The circuit arrangement shown in FIG. 1 shows a resonant converter 1having an inverter 2 which is here designed as a chopper and converts aDC voltage (not shown) into an AC voltage i.e. in this case chopped DCvoltage Us. The inverter 2 is coupled by a capacitor to a transformer 4,which has one primary winding 5 and two secondary windings 6 a and 6 b.The secondary windings 6 a and 6 b have different winding directions, sothat given a positive voltage Up on the primary winding 5 the voltageUsa generated on the secondary winding 6 a is also positive, whereasgiven a positive voltage Up, the dropping voltage Usb on the secondarywinding 6 b is negative. The transformer 4 has a common transformer coreboth for the primary winding 5 and for the secondary windings 6 a and 6b. A current flowing through the capacitor 3 in the primary winding 5 isdenoted by Ic.

The secondary winding 6 a is coupled by way of a diode Da and an outputfilter Fa to an output 7 a, on which an output voltage Ua is dropping.The secondary winding 6 b is connected by a diode Db and a filter Fb toan output 7 b, on which an output voltage Ub is dropping. The converter1 furthermore contains a feedback loop with a regulating circuit 8,which is coupled on the input side to the outputs 7 a and 7 b of theconverter 1 and on the output side to the inverter 2. The regulatingcircuit 8 sets the frequency and the duty cycle of the voltage Ussupplied by the inverter 2 as a function of the voltages Ua and Ubpresent on the outputs 7 a and 7 b, in order to regulate the outputvoltages Ua and Ub to desired predefined voltage values.

In the resonant converter 1, the capacitor 3, the main inductance andthe leakage inductances of the transformer 4 constitute resonant circuitelements, which are induced to oscillate by the a-c voltage Us andproduce a corresponding behavior of the current Ic flowing into thecircuit part that includes the resonant circuit elements and of thevoltage Up dropping on the primary winding. In the case of positivevoltage values of the voltage Up, a current Ia is generated, which flowsthrough the diode Da to the filter Fa for the time during which, in thisoperating state, the voltage Usa exceeds the voltage present on theinput of the filter Fa minus the diode forward voltage over the diodeDa. If the voltage Up on the primary winding 5 has positive voltagevalues, no current is generated by the secondary winding 6 b, since thediode Db blocks in this case.

In the event of negative voltage values of the voltage Up there is apositive voltage Usb present on the secondary winding 6 b and a negativevoltage Usa on the secondary winding 6 a. In this case a current Ib isgenerated, which flows from the secondary winding 6 b through the diodeDb to the output filter Fb for the period of time during which, in thisoperating state, the voltage Usb exceeds the voltage present on theinput of the filter Fb minus the diode forward voltage over the diodeDb.

FIG. 2 shows a design variant of the inverter or chopper 2 in FIG. 1. Anactuating signal 20, here represented by a pulse sequence, generated bythe regulating circuit 8, is fed to a half-bridge driver circuit 21,which generates from the actuating signal 20 control signals 22 and 23for the switching elements 24 and 25, which form a half-bridge circuit.The switching elements 24 and 25 are designed as MOSFET transistors. Thecontrol signals 22 and 23 are fed to gate connections (controlconnections) of the transistors 24 and 25. The inverter 2 converts a d-cvoltage U_(DC) into the a-c voltage Us by alternately switching theswitching elements 24 and 25 on and off. The d-c voltage U_(DC) isgenerated, in power supply units/power packs/chargers, for example, fromthe a-c voltage of an a-c voltage mains by means of rectifiers.

FIGS. 3A to 3C show design variants of the output filters Fa and Fb ofthe resonant converter 1. These have a connection A, which is connectedto the diodes Da and Db. The connections B and C are connected to theoutputs 7 a and 7 b of the converter 1. The filter according to FIG. 3only contains a capacitor 30. The output filter according to FIG. 3Bincludes two capacitors 31 and 32 and one inductance 33. The outputfilter according to FIG. 3C contains a capacitor 34, an inductance 35and a diode 36.

FIG. 4 shows an equivalent circuit diagram for the resonant converter 1in FIG. 1, in which the transformer 4 has been replaced by a transformerequivalent circuit diagram. Here the electrical function of thetransformer 4 may essentially be represented by a primary-side leakageinductance Lrp, a main inductance Lh, a secondary-side leakageinductance Lrsa for the secondary winding 6 a and a secondary-sideleakage inductance Lrsb for the secondary winding 6 b. The filters Faand Fb are here assumed as ideal and not shown, as is the regulatingcircuit 8. Loads Ra and Rb are connected to outputs 7 a and 7 b of theconverter 1.

FIGS. 5 to 7 show how it is possible to regulate the output voltages Uaand Ub by adjusting the frequency f0 and/or the cycle period t0=1/f0 andthe duty cycle of the a-c voltage Us. The duty cycle is here determinedby the period of time tsH and tsL, the upper switching element 24 beingswitched on and the lower switching element 25 being switched off duringa period of time tsH, and the upper switching element 24 being switchedoff and the lower switching element 25 being switched on during a periodof time tsL. The duty cycle is obtained as tsH/t0. The characteristicsof the a-c voltage Us, of the current Ic through the capacitor 3, of thecurrent Ia through the main inductance La of the transformer 4, of thecurrent Ia delivered by the secondary winding 6 a and of the current Ibdelivered by the secondary winding 6 b are represented for each of twoperiods of time t0. All winding ratios in the underlying exampleaccording to the equivalent circuit in FIG. 4 are assumed to be one;furthermore, Lrsa is here equal to Lrsb.

FIG. 5 shows the operating state in which the frequency f0=1/t0 is setto 1.47 times fr, fr being the resonant frequency of the converter 1 andbeing approximately determined as${fr} = {\frac{1}{2\pi}\sqrt{\frac{1}{{C(3)}\left\lbrack {{Lrp} + {Lh}} \right\rbrack}}}$

C(3) being the capacitance of the capacitor 3. In the operating instanceaccording to FIG. 5 the duty cycle is selected as 50%. In this operatingstate the current characteristics of Ia and Ib are generated withsubstantially identical half-waves during the time periods tsH and tsLrespectively. In the operating state according to FIG. 6 the frequencyf0=1/t0 is increased 1.53 times fr. The duty cycle is reduced to 40%.The characteristic of the current Ia has remained substantiallyidentical to the operating state in FIG. 5. The characteristic of thecurrent Ib now has half-waves with reduced amplitude, so that the powercarried to the output 7 b by the secondary winding 6 b is reduced. FIG.7 shows an operating instance with a frequency f0=1/t0 equal to 1.55times fr and a duty cycle of 65%. In this operating instance the currentIa is essentially reduced to zero and the amplitude of the half-waves ofIb increased in comparison to FIG. 6, so that in this operating instancethe secondary winding 6 a carries no power to the output 7 a but, incomparison to FIG. 6, secondary winding 6 b carries increased power tooutput 7 b.

The examples of operating states according to FIGS. 5 to 7 show thatwith the converter circuit according to the invention a highly variableadjustment to different loads of the various converter outputs ispossible. With the converter according to the invention it is possible,in particular, to achieve small tolerances of the output voltages evenin the case of low output voltages and high output currents.

FIGS. 8 and 9 show variants of the converter 1 in FIG. 1, which aredenoted by 1′ and 1″. In both variants the two secondary windings 6 aand 6 b are electrically coupled to each other; in this instance theyare connected to a common ground potential. In the embodiment of theconverter 1 according to FIG. 1 the secondary windings 6 a and 6 b areelectrically separated from each other. In FIG. 8, moreover, as afurther variant, an additional external inductance L1 is provided, whichis arranged on the primary side of the transformer 4 between thecapacitor 3 and the primary winding 5 and acts as an additionalinductive resonant circuit element in addition to the inductance of thetransformer 4. In the given type of transformer 4 with specifictransformer inductance this additional inductance enables the resonantfrequency of the converter to be adjusted. FIG. 9 shows additionalexternal inductances L2 a and L2 b on the secondary side of thetransformer 4. The inductance L2 a is arranged between the secondarywinding 6 a and the diode Ta, the inductance L2 b is connected betweenthe secondary winding 6 b and the diode Db. These two inductances alsoact as additional circuit elements and can be used to adjust thedesired—possibly asymmetrical—power distribution between the outputs innominal operation, for instance. Converter variants are obviously alsopossible, in which additional external inductances are provided both onthe primary side of the transformer 4 and on the secondary side of thetransformer 4.

FIG. 10 shows a converter variant 1′″ with a larger number of converteroutputs. In this instance the converter has four converter outputs. Inaddition to the primary winding 5 the transformer 4 now has two groupsof secondary windings with different winding directions (indicated bythe letters a and b), which comprise the secondary windings 6 a 1 and 6a 2 on the one hand and the secondary windings 6 b 1 and 6 b 2 on theother. The secondary windings are connected via diodes Da1, Da2, Db1 andDb2 with output filters Fa1, Fa2, Fb1 and Fb2 to the converter outputs,which carry output voltages Ua1, Ua2, Ub1 and Ub2. The output voltagesUa1 and Ub1 are fed as measured variables to the regulating circuit 8.The regulating circuit 8 therefore in this case evaluates two outputvoltages, the one output voltage Ua1 being generated by the secondarywinding 6 a 1 from the group of secondary windings with the firstwinding direction. The other output voltage Ub1 fed to the regulatingcircuit 8 is assigned to the secondary winding 6 b 1 from the group ofsecondary windings having the opposite winding direction. Heretherefore, a measured variable, i.e. output voltage, is evaluated foreach of the two groups having secondary windings of different windingdirections and used for regulating purposes. This represents aparticularly simple and effective method of regulating the outputvoltages of the converter.

FIG. 11 shows that as measured variables the regulating circuitevaluates either the actual voltages on the converter outputs or thevoltages on the connected load of the converter, the latter beingreduced compared to the corresponding output voltages, owing to voltagedrops on the leads between the converter and the loads. Examples of bothvariants are represented in FIG. 11. The converter outputs here carrythe two output voltages Ua and Ub, to each of which a load Ra and a loadRb is connected. The connecting leads between the converter outputsupplying the output voltage Ua and the load Ra are represented here bya block 31. The connecting leads between the output of the convertersupplying the output voltage Ub and the load Rb are represented by theblock 32.

FIG. 12 shows an example of embodiment of the regulating circuit 8. Afirst measuring signal Va and a second measuring signal Vb, whichcorrespond to output voltages Ua and Ub and Ua1 and Ub1 respectively,are fed to the two inputs of the regulating circuit. The measuringsignals Va and Vb are compared with reference signals Varef and Vbref.Subtracters 100 and 101 are used here. The subtracter 100 delivers thedifference Varef−Va to a circuit block 102. The subtracter 101 deliversthe difference Vbref−Vb to a circuit block 103. The circuit blocks 102and 103 include amplifiers and scaling circuits, so that the differencesignal supplied by the subtracter 100 is multiplied by a factor KA andthe difference signal supplied by the subtracter 101 by a factor KB.Here in this example of embodiment the following relationship applies:kA·Varef≅kB·Vbref

The output signals from the circuit blocks 102 and 103 are furtherprocessed by an adder 104 and a subtracter 105. The adder 104 adds theoutput signals from the circuit blocks 102 and 103 together and deliversits output signal to a frequency controller 106, which is designed, forexample, as a PID controller. The difference signal delivered by thesubtracter 105 is fed to a duty cycle controller 107, which is alsodesigned, for example, as a PID controller. A signal generator circuit108 now generates the regulation signal 20 supplied to the inverter 2 bythe regulating circuit 8, the regulation signal here being a pulse-widthmodulated signal. The frequency of the signal 20, which determines thefrequency of the a-c voltage Us of the resonant converter, is set by theoutput signal of the frequency controller 106. The duty cycle of thesignal 20, which determines the duty cycle of the a-c voltage Us, isadjusted by the duty cycle controller 107.

If the value of the measuring signal Va, for example, is reduced in theregulating circuit according to FIG. 12, so that Va becomes <Varef, thisleads on the one hand to a reduction of the frequency set by thecontroller 106 and hence, according to the behavior of a resonantconverter, to a tendency to increase on the part of the output voltagesgenerated by the resonant converter. On the other hand, however, theerror produced in this case also causes a reduction of the duty cycle ofthe signal 20 and the a-c voltage Us determined by the controller 107.This occurs, for example, in the operating state according to FIG. 6,where the power carried to the output 7 a by the secondary winding 6 ais increased in relation to the power carried to the output 7 b by thesecondary winding 6 b.

If in another instance, for example, the measuring signal Vb or thecorresponding output voltage Ub is reduced, this likewise leads to areduction of the frequency of the signals 20 or the frequency of the a-cvoltage Us. In this case, however, the controller 107 brings about anincrease of the duty cycle of the signal 20 and the duty cycle of thea-c voltage Us, so that in this operating instance the powerdistribution is modified so that the power carried to the output 7 b isincreased in comparison to the power carried to the output 7 a. Thecontrol characteristic also applies analogously to the design variantshaving more than two converter outputs.

FIG. 13 shows a circuit arrangement comprising the components of theregulating circuit 8 mentioned above and is complemented by an overloadprotection circuit and an overvoltage protection circuit; furthermorethe half bridge driver circuit 21 forms part of this circuitarrangement.

The circuit arrangement shown in FIG. 13 is supplied with the measuringsignals Va and Vb on the input side. An adder/subtracter device 201 issupplied with the measuring signal Va and a reference signal Varef. Anadder/subtracter device 202 is supplied with the measuring signal Vb anda reference signal Vbref. Furthermore, comparing devices 203 and 204 arearranged as comparators. The comparator 203 compares the measuringsignal Va with a maximum value Vamax. The comparator 204 compares themeasuring signal Vb with a maximum value Vbmax. If the measuring signalVa exceeds the maximum value Vamax or if the measuring signal Vb exceedsthe maximum value Vbmax, it is a case of overvoltage. For the case wherethe measuring signal Va exceeds the maximum value Vamax, the outputvoltage of the comparator 203 jumps from its minimum value Vkmin to itsmaximum value Vkmax. By weighting Vkmax with a weight Wa, an adaptationvalue 205 is generated which is applied to the adder/subtracter device202. For the case where the measuring signal Vb exceeds the maximumvalue Vbmax, the output voltage of the comparator 204 jumps from itsminimum value Vkmin to its maximum value Vkmax. By weighting Vkmax witha weight Wb, an adaptation value 206 is generated which is applied tothe adder/subtracter device 201.

The adder/subtracter device 201 forms the difference between thereference signal Varef and the measuring signal Va and adds theadaptation value 206 to this difference. The adder/subtracter device 202forms the difference between the reference signal Vbref and themeasuring signal Vb and adds the adaptation value 205 to thisdifference. The outputs of the adder/subtracter devices 201 and 202 areconnected to a circuit block 207 which comprises the components 102,103, 104, 105, 106 and 107 of the regulating circuit 8 shown in FIG. 12i.e. the outputs of the adder/subtracter devices 201 and 202 areconnected to the inputs of the circuit blocks 102 and 103. The outputsignals 208 and 209 of the circuit block 207 i.e. the output signals ofthe controllers 106 and 107 are applied to the signal generator circuit108 via two optocouplers 210 and 211 which cause a potential isolationto the signal generator circuit 108, which signal generator circuit 108generates the regulation signal 20 and sets its frequency and duty cyclein dependence on the signals 208 and 209. The regulation signal 20 isconverted as described above into control signals 22 and 23 by the halfbridge driver circuit.

The circuit arrangement in FIG. 13 further includes a comparator circuit212 which evaluates the respectively set duty cycle δ of the regulationsignal 20. The duty cycle represents the power distribution over thevarious converter outputs of the respective converter. The comparatorcircuit 212 determines whether the duty cycle δ lies in a range betweena predefinable minimum duty cycle value δmin and a predefinable maximumduty cycle value δmax. If the duty cycle δ lies outside the rangebetween δmin and δmax—which is the case when there is overload(particularly a short-circuit at a converter output)—the comparatorcircuit 212 causes control information to be delivered by the signalgenerator circuit 108 to the half bridge driver circuit of therespective resonant converter, the control information causing thecontrol signals 22 and 23 to be switched off and thus the respectiveresonant converter to be switched off. In the present case the controlinformation is transferred because the regulation signal 20 and thecontrol signals 22 and 23 are switched off, which is the simplestsolution for the transmission of control information. After the controlinformation has been delivered, the connected converter is switched off.

In the case of overvoltage i.e. when a converter output voltage exceedsa predefined permissible maximum value, so that Va becomes higher thanVaref or Vb becomes higher than Vbref, the adding together of theadaptation values 205 and 206 in the adder/subtracter devices 201 and202, respectively, forces the duty cycle δ to be situated outside therange δmin<δ<δmax. As described above, this leads to the release ofcontrol information which here causes the connected converter to beswitched off.

Blocks 213 and 214 indicate how circuit portions of the circuitarrangement shown in FIG. 13 can be preferably combined by means of oneor a plurality of integrated circuits; block 213 and/or block 214 arethen arranged by an integrated circuit. Block 213 comprises the circuitportions referred to as 21, 108, 212, 213, δmax and δmin; block 213 issupplied on its input side with the output signals from the optocoupler210 and 211 and on the output side the control signals 22 and 23 areproduced. Block 214 comprises the circuit portions referred to as Varef,Vbref, 201, 202, 203, 204, 205, Wa and Wb. Block 214 takes up on theinput side the measuring signals Va and Vb; on the output side the block214 delivers the signals 208 and 209 to the optocouplers 210 and 211.

1. A circuit arrangement comprising a regulating circuit (8) which isused for generating a pulse-width modulated regulation signal (20) independence on two measuring signals (Va, Vb) present on inputs of theregulating circuit (8) and comprising a comparator circuit (212) forcomparing the duty cycle (δ) of the regulation signal (20) with apredefinable maximum duty cycle value (δmax) and a predefinable minimumduty cycle value (δmin), said predefinable maximum and minimum dutycycle values (δmax and δmin) being input to said comparator circuit(212), wherein if the duty cycle (δ) is outside the range between themaximum duty cycle value (δmax) and the minimum duty cycle value (δmin)the circuit arrangement produces control information that corresponds tothis exceeding of the range.
 2. A circuit arrangement as claimed inclaim 1, characterized in that the control information is generated byswitching off the regulation signal (20).
 3. A circuit arrangement asclaimed in claim 1, characterized in that a first comparator device(203) is provided for comparing one (Va) of the two measuring signalswith a first maximum value (Vamax), an adaptation of the duty cycle (δ)caused by the generation of the control information taking place whenthe first maximum value (Vamax) is exceeded.
 4. A circuit arrangement asclaimed in claim 3, characterized in that the second comparator device(204) is provided for comparing the other one (Vb) of the two measuringsignals with a second maximum value (Vbmax), an adaptation of the dutycycle (δ) caused by the generation of the control information takingplace when the second maximum value (Vbmax) is exceeded.
 5. A circuitarrangement as claimed in claim 4, characterized in that a firstadder/subtracter device (201) is provided which forms a first difference(Varef−Va) between one (Va) of the two measuring signals and a firstreference value (Varef), in that a second adder/subtracter device (202)is provided for forming a second difference (Vbref−Vb) between the otherone (Vb) of the two measuring signals and a second reference value(Vbref), in that for the case where the first one (Va) of the twomeasuring signals exceeds a predefinable first maximum value (Vamax),the second difference (Vbref−Vb) is adapted by the secondadder/subtracter device (202) by a predefinable first adaptation value(205), in that for the case where the second one (Vb) of the twomeasuring signals exceeds a predefinable second maximum value (Vbmax),the first difference (Varef−Va) is adapted by the first adder/subtracterdevice (201) by a predefinable second adaptation value (206), in thatthe regulation signal (20) is adapted in dependence on the outputsignals of the adder/subtracter devices (201, 202) which output signalsare determined by the first and second differences (Varef−Va, Vbref−Vb)and by the first and second adaptation values (205, 206).
 6. A circuitarrangement as claimed in claim 1, characterized in that the circuitarrangement comprises two sub-circuits (213, 214) which are mutuallycoupled by two optocouplers (210, 211).
 7. A resonant convertercomprising a circuit arrangement as claimed in claim
 1. 8. An integratedcircuit (213) comprising a signal generator (108) for generating apulse-width modulated regulation signal (20) and including a comparatorcircuit (212) for comparing the duty cycle (δ) of the regulation signal(20) with a predefinable maximum duty cycle value and a predefinableminimum duty cycle value, said predefinable maximum and minimum dutycycle values being input to said comparator circuit (212), wherein ifthe duty cycle (δ) is outside the range between the maximum duty cyclevalue (δmax) and the minimum duty cycle value (δmin) the integratedcircuit (213) delivers control information that corresponds to thisexceeding of the range.
 9. An integrated circuit as claimed in claim 8,characterized in that the circuit (213) also includes a half bridgedriver circuit (21).
 10. A resonant converter comprising an integratedcircuit as claimed in claim
 8. 11. An integrated circuit, comprising afirst adder/subtracter device (201) which forms a first difference(Varef−Va) between a first measuring signal (Va) and a first referencevalue (Varef), and a second adder/subtracter device (202) which forms asecond difference (Vbref−Vb) between a second measuring signal (Vb) anda second reference value (Vbref), in that for the case where the firstmeasuring signal (Va) exceeds a predefinable first maximum value(Vamax), the second difference (Vbref−Vb) is adapted by the secondadder/subtracter device (202) by a predefinable first adaptation value(205), in that for the case where the second measuring signal (Vb)exceeds a predefinable second maximum value (Vbmax), the firstdifference (Varef−Va) is adapted by the first adder/subtracter device(201) by a predefinable second adaptation value (206).
 12. A resonantconverter comprising an integrated circuit as claimed in claim 11.